Cold hardiness & minimum temperature

Is Delphinium grandiflorum 'Blue Butterfly' (Delphinium grandiflorum 'Blue Butterfly')cold hardy? Hardiness zone & min temp

Also called Blue Butterfly delphinium, Chinese delphinium.

More about delphinium grandiflorum 'blue butterfly'

About Delphinium grandiflorum 'Blue Butterfly'

Delphinium grandiflorum 'Blue Butterfly' · also called Blue Butterfly delphinium, Chinese delphinium · flowering

'Blue Butterfly' is a dwarf Chinese delphinium grown for masses of brilliant gentian-blue flowers on airy, branching stems in summer. Far shorter than border delphiniums at 30-40 cm, it suits fronts of beds, pots and gravel gardens, needs no staking, and flowers fast from seed. Like all delphiniums, it is toxic to cats and dogs.

Cold limit: USDA 3-8 · RHS H5 (-34 to 27°C)

Watch for — Crown rot in wet soil: Heavy, poorly drained ground rots this short-lived species fast. Plant in sharply drained soil or gritty container mix and avoid winter wet.

What delphinium grandiflorum 'blue butterfly''s hardiness rating actually means

Yes — delphinium grandiflorum 'blue butterfly' is genuinely cold hardy. Rated RHS H5 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 3-8 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −15 to −10 °C. Delphinium grandiflorum 'Blue Butterfly' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for delphinium grandiflorum 'blue butterfly' as it gets too cold:

It tolerates winter lows to about −15 to −10 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can delphinium grandiflorum 'blue butterfly' go outside or overwinter — and where?

Plant it out within USDA 3-8 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when delphinium grandiflorum 'blue butterfly' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Delphinium grandiflorum 'Blue Butterfly' hardiness — frequently asked questions

Is delphinium grandiflorum 'blue butterfly' cold hardy?

Yes — delphinium grandiflorum 'blue butterfly' is genuinely cold hardy. Rated RHS H5 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Delphinium grandiflorum 'Blue Butterfly' is hardy across USDA 3-8; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature delphinium grandiflorum 'blue butterfly' can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Delphinium grandiflorum 'Blue Butterfly' is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is delphinium grandiflorum 'blue butterfly'?

Delphinium grandiflorum 'Blue Butterfly' is rated USDA 3-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can delphinium grandiflorum 'blue butterfly' survive winter outside?

Plant it out within USDA 3-8 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to delphinium grandiflorum 'blue butterfly' below its minimum temperature?

It tolerates winter lows to about −15 to −10 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.